Pests & Diseases of Pine Trees

Pine trees and shrubs are members of the conifer family, a diverse group that grows in a variety of climates. They like full sun and well-drained soil and, once established, don’t require a lot of water. They vary widely in size, from the tiny 4-foot dwarf mugo pines (Pinus mugo), to the stately 100-foot white pine (Pinus strobes). Pines are generally easy to care for, but can be plagued by pests and diseases. Some of the more common include cankers, rusts, bark beetles and soft scales.


If your pine tree develops an area of dead, sunken tissue on its stems or branches, it could be afflicted with a canker disease. Foliage on infected limbs can turn yellow or brown and wilt, while infected bark can become discolored and ooze resin. Pines infected with canker diseases are also vulnerable to fungal diseases. Untreated canker diseases can spread, killing limbs or the entire tree. The best defense against canker diseases is to choose disease-resistant cultivars that are suited to your soil and climate. If existing pines become infected, prune out infected areas by cutting into healthy wood past the infection. Once the trunk is infected, pruning is of limited effect. Do not fertilize pines with cankers, as this can promote the spread of disease.


Rusts on pine trees look just like what their name implies: Infected areas develop dry red, orange or yellow pustules or spore masses. Some rusts cause cankers on bark, spots on foliage, and orange, gelatinous masses. Rusts can cause limbs and branches to die back, and, if untreated, can spread and kill the entire pine. “Witches brooms,” leaves and foliage that become dwarfed, distorted and discolored, can also be the result of rust infections. To combat rusts, don’t water pine shrubs from above, as this can cause spores to germinate. Clean up and dispose of infected needles, remove and dispose of infected branches as soon as you see them. Fungicides applied in the spring can reduce rust infections but frequent applications are required, which can be difficult.

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Bark Beetles

Bark beetles are common pine pests, with more than 600 species of bark beetles in North America and 200 species in California alone. The most common species are western pine beetles, engraver beetles and red turpentine beetles. If you suspect bark beetle infestation, peeling back the bark to expose beetle tunnels can help identify which beetle you’re dealing with. Western pine beetles attack pines mid-trunk then work their way up and down the tree in a spaghetti-like pattern. Red turpentine beetles attack the lowest parts of the trunk and the roots and tunnel out cave-like galleries then move downward. Engraver beetles attack pines near the top and make wishbone-shaped tunnels. Because beetles live under bark, insecticides are usually not effective against them. Cultural practices, such as selecting healthy trees that are suited to your environment, avoiding injuring pines which can allow beetles access through wounds, and thinning dense stands of trees are the best defenses.

Soft Scale Insects

Although scale insects don’t typically harm pines, they are a nuisance because they secrete honeydew, a sticky liquid that provides a place for black sooty mold to grow. Scales don't always look like typical insects -- adult females and immature nymphs don’t have recognizable body parts, don’t move and look like rounded, flat lumps. Adult males are tiny and only live for a few hours, so you will probably never see them. Irregular pine scale insects typically infect Monterey pines (Pinus radiata) but are also found on other pine species. Heavy scale infestation can cause foliage to yellow and drop but the major concern is the abundant production of honeydew. They rarely kill trees although they do reduce trees’ health and vigor. Scale insects are usually controlled by natural predators, unless ants, attracted to the honeydew, interfere. Applications of pesticides and narrow-range oils can control scales, but these also kill natural predators. Controlling ants is usually enough to allow natural predators to return and, in turn, control the scales.


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